The invention pertains to an apparatus for hyperthermic treatment which is especially well suited to deep hyperthermia, i.e. in cases where the part that has to be treated in a patient lies relatively deep within his body.
Hyperthermia is a method in which living biological tissues are heated, for example through the dissipation of an electro-magnetic wave applied to a part that has to be treated, using applicators laid out in the vicinity of this part. This method is used in the treatment of various diseases, especially in the treatment of cancer. In the example of the latter application, it is desirable to heat the tissues to be treated to temperatures of about 44.degree. C. to 45.degree. C. while at the same time avoiding, as far as possible, any marked increase in the temperature of the surrounding healthy tissues.
One of the problems that arise then is to accurately localize the heated area in relation to the area that to be treated. This condition is generally achieved satisfactorily in the treatment of superficial or shallow tumours since, in this case, the applicators placed on the patient's body are in the immediate vicinity of the area to be treated.
By contrast, in the treatment of deep-seated tumours (for example, intestinal, prostate or other such tumours), the problem of accurately localizing the power applied becomes far more acute, especially since that part of the patient which lies between two electrodes also includes healthy regions, and the problem is additionally complicated by the fact that a patient usually finds it very difficult to tolerate temperatures of more than 44.degree. C. in the cutaneous tissues.
The technique most widely used in hyperthermia is to do the heating by means of an electro-magnetic field at frequencies which are low enough not to be limited by skin effect which prevents penetration by these electro-magnetic fields when the frequencies are greater than, for example, 50 or 60 MHZ. The applicators comprise electrodes or conductor horns or wave guides, by means of which the electro-magnetic power is applied. In outline, the heated region is the region enclosed by the electrodes or, again, in the case of a conductor horn or a wave guide, the dimensions of the heated region are approximately equal to the crosswise dimensions of the applicator. It is thus possible, in theory, to modify the distribution of the power dissipated by bringing the dimensions and position of the electrodes into play. However, the use of this method comes up against practical difficulties owing to the fact that, in a given configuration of electrodes, the distribution of the dissipated power depends on the electrical properties of the tissues to be heated. It is furthermore observed that the distribution of the dissipated power can vary a great deal for apparently small variations in the nature of the tissues to be heated. Thus, in practice, to obtain heating that is as satisfactory as possible, the practitioner must, in the very course of the hyperthermic treatment, adjust the distribution of the dissipated power, notably on the basis of data communicated by temperature probes.
To this end, a method known in the prior art through the french patent application No. 83 08727, uses high-frequency generating means comprising at least three generators which function at one and the same frequency and according to adjustable relative phases, each generator being linked to an electrode. This configuration can be used to localize a more strongly heated zone in a space surrounded by the three electrodes. One of the disadvantages of this arrangement, in which generators work at one and the same frequency with well-defined mutual phase relations, lies in the fact that field interference effects can occur in the zone to be heated, in such a way that the mean power dissipated in a given volume can be greater or smaller than the sum of the mean values of power dissipated by each generator working on its own. The result of this may be major temperature differences between two points which are relatively close to each other, with prolonged and difficult adjustments having to be made to correct these differences.